<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <script>
        var obj = {
            a: 1,
            b: 2
        };
        var res = JSON.parse(JSON.stringify(obj));
        obj.a = 4;
        console.log(obj);
        console.log(res);
    </script>
</body>

</html>